"Marky P" wrote in message
...
On Wed, 1 Oct 2008 10:42:53 +0100, "David Looser"
wrote:


Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.

Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder


Faulty capacitors in power supplies usually make themselves apparent by such
problems as low voltage or excessive ripple on one or more of the output
lines, or rather more obviously by leaking electrolyte, bulging seals etc.
In view of the age of this unit your best bet is probably simply to replace
any suspect capacitors rather than bothering to try and test them.

David.

On Fri, 3 Oct 2008 16:47:49 +0100, "David Looser"
wrote:

"Marky P" wrote in message
.. .
On Wed, 1 Oct 2008 10:42:53 +0100, "David Looser"
wrote:


Since the OP has remained silent since his first post what he actually
wanted remains a mystery.

David.

Very sorry! I forgot made this post (someone over at alt.digital.tv
remined me). I want to test for faulty caps. It's in a power supply
unit in a 1980's professional multi-track tape recorder


Faulty capacitors in power supplies usually make themselves apparent by such
problems as low voltage or excessive ripple on one or more of the output
lines, or rather more obviously by leaking electrolyte, bulging seals etc.
In view of the age of this unit your best bet is probably simply to replace
any suspect capacitors rather than bothering to try and test them.

David.

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable. The caps were
replaced and the problem was rectified. Well, within a couple of
months the fault is back, and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Marky P.

"Marky P" wrote in message
...

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.

Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?

The caps were
replaced

All of them?

and the problem was rectified. Well, within a couple of
months the fault is back,

So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the result
of a broken PCB track, dry joint or poor connection somewhere that makes
contact when it wants too, and the "cure" last time was due to the physical
handling of the PSU causing this to make contact again, for a while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.

David.

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.

Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?

The caps were
replaced

All of them?

and the problem was rectified. Well, within a couple of
months the fault is back,

So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the
result of a broken PCB track, dry joint or poor connection somewhere that
makes contact when it wants too, and the "cure" last time was due to the
physical handling of the PSU causing this to make contact again, for a
while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.

Excatly what I thought.
Mind you they do a very good line of condensers on the planet Metaluna.
http://en.wikipedia.org/wiki/This_Island_Earth

--
Graham.

%Profound_observation%

"David Looser" wrote in message
...
"Marky P" wrote in message
...

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.

Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?

The caps were
replaced

All of them?

and the problem was rectified. Well, within a couple of
months the fault is back,

So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the
result of a broken PCB track, dry joint or poor connection somewhere that
makes contact when it wants too, and the "cure" last time was due to the
physical handling of the PSU causing this to make contact again, for a
while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.

David.


What's wrong with Bury St Edmunds? My designs generally work.......
S.
--
http://audiopages.googlepages.com

On Fri, 3 Oct 2008 21:28:09 +0100, "David Looser"
wrote:

"Marky P" wrote in message
.. .

Basically, there was a severe buzzing noise on the output and the
fault was traced to the PSU supply not being stable.

Is it a linear, or switch-mode? How many output rails are there? does the
instability affect them all, or only one or two?

Unfortunately I haven't looked at it myself, so I don't know.

The caps were
replaced

All of them?

Again, I'm not sure. Wouldn't've thought so.

and the problem was rectified. Well, within a couple of
months the fault is back,

So probably not capacitors then, unless it's the ones that got missed last
time. (Is the fault *exactly* the same?) Maybe the instability is the result
of a broken PCB track, dry joint or poor connection somewhere that makes
contact when it wants too, and the "cure" last time was due to the physical
handling of the PSU causing this to make contact again, for a while.

and instead of paying silly prices to one of
the very few tape machine repair guys around, my mate wanted me to fix
it if I could find the faulty caps. The last repair cost £500. The
tape machine is a Saturn Soundcraft, and aparently there is only one
person in the country who can repair them (he lives in Bury St.
Edmunds).

Unlikely. Unless the machine was designed on Saturn (or in Bury St Ed) any
competent repair technician ought to be able repair it.

David.


Marky P.